Genetics: immaculate misconception

Assessment of Consumers' Perception of Chicken Eggs Consumption and Associated Health Implications in the Volta Region of Ghana

Background:

Rather erroneously, eggs consumption is linked to increase in plasma cholesterol content and incidents of cardiovascular diseases, cancer, stroke, or diabetes. This misconception which is more pervasive particularly in sub-Saharan Africa, has led to very low patronage of eggs intake. In this study, egg consumption patterns, desired egg characteristics, and the extent to which the perception of eggs consumption as a health risk is entrenched among consumers in the Volta Region of Ghana, were examined.

Methods:

The study used primary data for the analysis and the 2-stage sampling technique was employed. First, 5 districts (Keta, Ho, Krachi East, Nkwanta South and North Tongu) were selected and afterward, a sample was randomly selected from each of the district. A well designed and pretested questionnaires were administered to the respondents.

Results:

It was found that cheaper price and deep yellow yolk were the most persuasive parameters that motivate consumer purchase. The relationship between educational level and awareness on cholesterol types was significant. More than half of the respondents held the view that egg intake results in an increase in serum cholesterol and leads to the incidence of serious health problems.

Recommendation:

This study proves the urgent need for a concerted national public education effort to raise awareness about the nutritional and health benefits of eggs intake. Success in such awareness creation will go a long way to greatly minimize acute malnutrition in the Ghana.

Cell lines derived from human parthenogenetic embryos can display aberrant centriole distribution and altered expression levels of mitotic spindle check-point transcripts

Human parthenogenetic embryos have recently been proposed as an alternative, less controversial source of embryonic stem cell (ESC) lines; however many aspects related to the biology of parthenogenetic embryos and parthenogenetic derived cell lines still need to be elucidated. We present here results on human cell lines (HP1 and HP3) derived from blastocysts obtained by oocyte parthenogenetic activation. Cell lines showed typical ESC morphology, expressed Oct-4, Nanog, Sox-2, Rex-1, alkaline phosphatase, SSEA-4, TRA 1-81 and had high telomerase activity. Expression of genes specific for different embryonic germ layers was detected from HP cells differentiated upon embryoid body (EBs) formation. Furthermore, when cultured in appropriate conditions, HP cell lines were able to differentiate into mature cell types of the neural and hematopoietic lineages. However, the injection of undifferentiated HP cells in immunodeficient mice resulted either in poor differentiation or in tumour formation with the morphological characteristics of myofibrosarcomas. Further analysis of HP cells indicated aberrant levels of molecules related to spindle formation as well as the presence of an abnormal number of centrioles and autophagic activity. Our results confirm and extend the notion that human parthenogenetic stem cells can be derived and can differentiate in mature cell types, but also highlight the possibility that, alteration of the proliferation mechanisms may occur in these cells, suggesting great caution if a therapeutic use of this kind of stem cells is considered.

Genetics, epigenetics and gene silencing in differentiating mammalian embryos

A highly complex pattern of differentiation involving maternal and embryonic factors characterizes the early development of mammalian embryos. These complex genetic and proteonomic patterns of early growth also involve various forms of gene silencing and tissue reprogramming. Understanding the nature of fundamental developmental events is hence essential to appreciate the significance of natural and induced forms of remodelling, damaged forms of gene expression and gene silencing during the initial stages of growth. Natural forms of remodelling include subtle genetic events involved in, for example, the changing nature of imprinting from before fertilization or the inactivation of one X chromosome in female blastocysts. Induced forms include the consequences of nuclear transfer and embryo cloning or the immediate effects of placing embryos in culture media. Animal and human studies are described in this paper, relating reprogramming to detailed embryological and clinical knowledge gained through the use of IVF, preimplantation genetic diagnosis and the establishment in vitro of stem cells. Attention concentrates on the consequences of variations in all growth stages from the formation of oocytes, through fertilization, the differentiation of blastocysts and early haemopoietic stages in mammalian species. Unique features of gene expression or gene modification are described for each developmental stage.

[Mutation mechanisms and their consequences]

The identification of mutations leading to human genetic diseases has grown into an intensive research field during the last few years. Through novel DNA analysis progress, it is now possible to determine the mutational spectrum for a given genetic disease and international databases are now available online. Genetic diagnosis of hereditary diseases has become an essential tool in genetic counselling and prenatal diagnosis. The knowledge of the deleterious mutation type and the molecular associated mechanism is fundamental in order to devise the optimal molecular diagnosis strategy. This review aims to present the various mutation categories involved in genetic diseases (single base-pair substitutions, small deletions or insertions, dynamic mutations, gross DNA lesions...) and to summarize our current knowledge about the main molecular mechanisms responsible for these mutations. Their deleterious consequences on gene expression, including transcription and transcript maturation, and protein loss or gain of function are also discussed in this review.

CDKN1C mutation in Wiedemann-Beckwith syndrome patients reduces RNA splicing efficiency and identifies a splicing enhancer

Wiedemann-Beckwith syndrome (WBS) is a human overgrowth disorder that is accompanied by an increased risk of embryonal tumors and is associated with dsyregulation of the imprinting of genes in chromosome 11p15.5. Maternally inherited mutations in the imprinted CDKN1C gene are known to be associated with WBS. We have identified a novel mutation in several members of a large family affected by WBS. The mutation is a G --> T change in a run of seven G's near the 5' splice site of intron 3. All obligate carriers and affected individuals carry the mutation, and in each affected case, the allele was inherited maternally, strongly suggesting a role in causing WBS. The mutation is located in a poly-G tract in the intron; intronic G-rich sequences in other genes have been shown to have a role in promoting splicing. In transfected 293HEK cells, we found that the G --> T mutation reduced splicing efficiency. Mutation of all seven G's in the poly-G tract further reduced splicing efficiency, supporting a role for the G-tract as a splicing enhancer. The fibroblasts of one affected patient showed a similar reduction in splicing efficiency. Maternal monoallelic expression of CDKN1C was verified in this patient cell line. However, the total amount of spliced message was not reduced by the mutation in spite of the reduced efficiency of splicing. We discuss the possible role of the splicing defect in the pathogenesis of WBS in this pedigree.

DNA methylation in the preimplantation embryo: the differing stories of the mouse and sheep

In mammals, active demethylation of cytosine methylation in the sperm genome prior to forming a functional zygotic nucleus is thought to be a function of the oocyte cytoplasm important for subsequent normal development. Furthermore, a stepwise passive loss of DNA methylation in the embryonic nucleus has been observed as DNA replicates between two-cell and morula stages, with somatic cell levels of methylation being re-established by, or after the blastocyst stage when differentiated lineages are formed. The ability of oocyte cytoplasm to also reprogram the genome of a somatic cell by nuclear transfer (SCNT) has raised the possibility of directing reprogramming of a somatic nucleus ex ovo by mimicking the epigenetic events normally induced by maternal factors from the oocyte. Whilst examining DNA methylation changes in normal sheep fertilization, we were surprised to observe no demethylation of the sheep male pronucleus at any point in the first cell cycle. Furthermore, using quantitative image analysis, we observed limited demethylation of the sheep embryonic genome only between the two- and eight-cell stages and no evidence of remethylation by the blastocyst stage. We suggest that the dramatic differences in DNA methylation between the sheep and other mammalian species examined call in to question the requirement and role of DNA methylation in early mammalian embryonic development.

Tribute to Georgeanna and Howard Jones

This tribute is divided into three sections. The first of these is a description of six weeks of research involving Georgeanna and Howard Jones and me over a few weeks in Johns Hopkins in 1965. Initially, it describes details of preliminary work and then completion of the maturation programme of the mature human oocyte and the first serious attempts at IVF. Scientific discoveries in those exciting weeks contributed to the earliest beginnings of IVF. A second section on knowledge of the human preimplantation embryo today concentrates on the problem of poor-quality embryos and how to overcome it, and on new knowledge on the regulation of human embryonic development. Lastly, the ethics of assisted conception are debated in relation to early practice and to some international features of modern ethical adjudication. A brief conclusion describes some of the friendships initiated in Johns Hopkins and still intact today.

Cell differentiation in the preimplantation human embryo

This brief paper analyses current knowledge on gene expression in individual blastomeres of preimplantation mammalian embryos. Initially, current knowledge on axes and cleavage planes in mammalian eggs and embryo blastomeres is described, together with gene and system homologies with flies and nematodes, and their influence on differentiation. Stress is placed on the need to study individual blastomeres, and even specific components within blastomeres. Examples of published work concentrate on the possible allocation of a single founder blastomere for trophectoderm, which contains large amounts of maternal leptin, STAT3 and other proteins positioned at the animal pole. The recent discovery that single human blastomeres in cleaving embryos contain high levels of HCGbeta mRNA and LHbeta mRNA suggests these are also trophectoderm foundation cells. It is now essential to discover if the maternal proteins leptin/STAT3 and maternal/embryonic HCGbeta transcripts locate to the same blastomere. Problems in jointly identifying maternal proteins and embryonic and maternal transcripts for specific proteins within one cell, and the nature of early cell allocation in mouse and human embryo, are discussed.

Aspects of the molecular regulation of early mammalian development

Many regulatory systems operate in the early mammalian embryo. This brief overview surveys several systems and their integration including polarities and axes, left-right differentiation, timers in cells, tissues and in gene expression, and imprinting. Polarities are essential from the very earliest stages of oocyte formation, and maintain their significance until blastocyst stages and beyond. They determine cleavage axes and the distribution of maternal proteins in the oocyte, distinct distributions being identified at the animal pole especially. Left-right axes are no doubt expressed from the earliest embryonic stages, and perhaps even in determining slight differences in the axes of cleavage and of maternal protein distribution. Timers, equally fundamental, have been demonstrated to control many functions in oocytes and embryos. Many fundamental processes in early mammalian oocytes and embryos are closely timed. They are classified into circadian rhythms, hourglass timers, clocks regulating major aspects of development including transcription, longevity via telomere clocks and long-range systems. Imprinting and methylation, increasingly important in establishing stable phenotypes in early embryos, might develop abnormally under some circumstances including intracytoplasmic sperm injection and cloning. A general summary briefly describes some other aspects of regulation, especially chromosomal anomalies in human embryos.

Epigenetics in cancer: implications for early detection and prevention

Knowledge of the molecular events that occur during the early stages of cancer has advanced rapidly. The initiation and development of cancer involves several molecular changes, which include epigenetic alterations. Epigenetics is the study of modifications in gene expression that do not involve changes in DNA nucleotide sequences. Modifications in gene expression through methylation of DNA and remodelling of chromatin via histone proteins are believed to be the most important of the epigenetic changes. The study of epigenetics offers great potential for the identification of biomarkers that can be used to detect and diagnose cancer in its earliest stages and to accurately assess individual risk. There has been a recent surge of interest among researchers as variations in the methylation of DNA have been shown to be the most consistent molecular changes in many neoplasms. An important distinction between a genetic and an epigenetic change in cancer is that epigenetic changes can be reversed more easily by use of therapeutic interventions. The discovery of these basic premises should stimulate much future research on epigenetics.

Cardiovascular and diabetes mortality determined by nutrition during parents' and grandparents' slow growth period

Overfeeding and overeating in families are traditions that are often transferred from generation to generation. Irrespective of these family traditions, food availability might lead to overfeeding, in its turn leading to metabolic adaptations. Apart from selection, could these adaptations to the social environment have transgenerational effects? This study will attempt to answer the following question: Can overeating during a child's slow growth period (SGP), before their prepubertal peak in growth velocity influence descendants' risk of death from cardiovascular disease and diabetes? Data were collected by following three cohorts born in 1890, 1905 and 1920 in Overkalix parish in northern Sweden up until death or 1995. The parents' or grandparents' access to food during their SGP was determined by referring to historical data on harvests and food prices, records of local community meetings and general historical facts. If food was not readily available during the father's slow growth period, then cardiovascular disease mortality of the proband was low. Diabetes mortality increased if the paternal grandfather was exposed to a surfeit of food during his slow growth period. (Odds Ratio 4.1, 95% confidence interval 1.33-12.93, P=0.01). Selection bias seemed to be unlikely. A nutrition-linked mechanism through the male line seems to have influenced the risk for cardiovascular and diabetes mellitus mortality.

Transdifferentiation and nuclear reprogramming in hematopoietic development and neoplasia

Cell transplantation and tissue regeneration studies indicate a surprisingly broad developmental potential for lineage-committed hematopoietic stem cells (HSCs). Under these conditions HSCs transition into myocytes, neurons, hepatocytes or other types of nonhematopoietic effector cells. Equally impressive is the progression of committed neuronal stem cells (NSCs) to functional blood elements. Although critical cell-of-origin issues remain unresolved, the possibility of lineage switching is strengthened by a few well-controlled examples of cell-type conversion. At the molecular level, switching probably initiates from environmental signals that induce epigenetic modifications, resulting in changes in chromatin configuration. In turn, these changes affect patterns of gene expression that mediate divergent developmental programs. This review examines recent findings in nuclear reprogramming and cell fusion as potential causative mechanisms for transdifferentiation during normal and malignant hematopoiesis.